Playground · Build · 2026

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Old vs New Tax Regime Calculator — for FY 2025-26, no login wall

For Indian salaried individuals trying to decide which regime to opt for. Full slab logic for both, all the standard deductions (80C, 80D, HRA, home loan interest), and a clear breakdown of which saves you more and by how much. No login, no email gate.

Role

Designer · Frontend Developer

Timeline

1 weekend

Team

1 person

Scope

Frontend, Indian tax calculation

Why this exists

Every March, the same conversation. A salaried friend asks: "Should I be on the old regime or the new one?" Every existing calculator I send them is one of two things — a financial-advisor lead-magnet that asks for a phone number, or a journalist's story with a generic example that doesn't match their salary.

The math is not hard. It's a slab calculation, plus deductions, plus a comparison. The reason a simple, fast, no-login calculator doesn't exist is that there's no business model in it. Which is exactly why it's worth building.

What it does

Six inputs:

  1. Annual gross salary (CTC)
  2. Employer PF contribution (auto-detected if you check the standard 12% box)
  3. Section 80C contributions — PPF, ELSS, life insurance premium, principal home loan
  4. Section 80D — health insurance premium, self and parents
  5. HRA — rent paid, basic salary component, metro/non-metro flag
  6. Home loan interest — Section 24

Two outputs side-by-side: tax payable under the old regime, tax payable under the new regime. Difference highlighted in colour. A one-line summary: "On new regime, you pay ₹47,200 less. Switch."

A "show the working" toggle that walks through every slab and every deduction so the user can verify the math themselves.

How it's built

  • Frontend-only. Static export. Hosts on Vercel free tier.
  • All math runs client-side. Zero data leaves the browser.
  • Slab tables and deduction limits in a slabs.ts file — easy to update next financial year.

What it isn't

Not a tax-filing service. Not a CA replacement. Not for capital gains or business income.

Specifically for salaried individuals deciding between regimes. That's a constrained-enough problem that one good calculator can solve it for everyone.

Why it doesn't exist yet

The blocking issue is trust. Tax math is the kind of thing where users want a credible source. A no-name calculator on a personal portfolio site has to earn that credibility — by showing the working, citing the slab tables to the actual government source, and being transparent about the assumptions.

I want to ship this with a "verified against the official income tax department calculator" badge — which means running 50-odd test cases and matching outputs to the rupee. That's the work I haven't done yet.